Workpiece mounting apparatus for an internal grinding machine

ABSTRACT

A workpiece mounting apparatus in which a measuring gauge for measuring a cylindrical bore of a workpiece is provided with a tapered portion thereon and is fixedly mounted on a shiftable rod which in turn is slidably mounted within a spindle. The measuring gauge projects from a reference face plate on a chuck housing a predetermined amount as a result of axial movement of the shiftable rod so as to align the axis of the workpiece with the axis of the spindle. When the workpiece is clamped on the reference plate by clamping means, the tapered portion of the measuring gauge is engaged with the cylindrical bore of the workpice. Thus, axial alignment between the spindle and the workpiece is established by confirming the engagement of the tapered portion of the measuring gauge and the bore of the workpiece by means of a detector and thereafter, the tapered portion thereof is extracted from the cylindrical bore of the workpiece.

[ Apr. 1,1975

1 1 WORKPIECE MOUNTING APPARATUS FOR AN INTERNAL GRINDING MACHINE Inventors: Makoto Kikuchi, Kariya; Ikuo Otsu,

Toyota, both of Japan Assignee: Toyoda Koki Kabushiki Kaisha,

Kariya-shi, Aichi-ken, Japan Filed: Oct. 5, 1973 Appl. No.: 403,869

[30] Foreign Application Priority Data Oct. 19, 1972 Japan 47-120094 References Cited UNITED STATES PATENTS Dix 51/236 X Primary ExaminerHarold D. Whitehead Attorney, Agent, or FirmOblon, Fisher, Spivak, McClelland & Maier [57] ABSTRACT A workpiece mounting apparatus in which a measuringgauge for measuring a cylindrical bore of a workpiece is provided with a tapered portion thereon and is fixedly mounted on a shiftable rod which in turn is s1idab1y mounted within a spindle. The measuring gauge projects from a reference face plate on a chuck housing a predetermined amount as a result of axial movement of the shiftable rod so as to align the axis of the workpiece with the axis of the spindle. When the workpiece is clamped on the reference plate by clamping means, the tapered portion of the measuring gauge is engaged with the cylindrical bore of the workpice. Thus, axial alignment between the spindle and the workpiece is established by confirming the engagement of the tapered portion of the measuring gauge and the bore of the workpiece by means of a detector and thereafter, the tapered portion thereof is extracted from the cylindrical bore of the workpiece.

6 Claims, 6 Drawing Figures PATENTEB APR 1 1975 ziLi l U! 3 WORKPIECE MOUNTING APPARATUS FOR AN INTERNAL GRINDING MACHINE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to a workpiece mounting apparatus, and more particularly to an improved apparatus for establishing axial alignment between a workpiece and a spindle.

2. Description of the Prior Art In a conventional internal grinding machine, the workpiece is clamped by means of a chucking device such as an electromagnetic chuck or diaphragm chuck to thereby align the same, with the axis of a spindle.

In such a machine, when clamped, the axis of the workpiece is aligned with the axis of the spindle with reference to the outer diameter thereof and therefore, the axis of the cylindrical bore of the workpiece is apt to deviate from the axis of the spindle. Consequently, a degree of grinding accuracy is decreased due to the fact that the axis of the workpiece is not always aligned with the axis of the spindle and further, the amount of grinding of the workpiece differs at various places around the bore thereof. Moreover, if a thin cylindrical workpiece of a workpiece having a notched portion on the periphery thereof is supported in the diaphragm chuck, the shape of the workpiece is changed, thereby having a further decrease in accuracy in the degree of grinding.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a new and improved workpiece mounting apparatus.

Another object of the present invention is to provide a workpiece mounting apparatus in which the axis of a workpiece is exactly and efficiently aligned with the axis of a spindle with reference to a measuring gauge on a shiftable rod when the workpiece is clamped on a reference face plate of a chuck housing by means of clamping claws.

Still another object of the present invention is to provide a workpiece mounting apparatus wherein a workpiece is positively clamped on a reference face plate of a chuck housing by means of clamping claws in accordance with axial movement of an operating member without deforming the workpiece.

The foregoing and other objects are attained through the provision of a workpiece mounting apparatus according to the present invention which features a measuring gauge fixedly mounted on a s hiftable rod within a spindle such that the axis of a workpiece coincides with the axis of the spindle. Firstly, the tapered portion of the measuring gauge projects from a reference face plate of a chuck housing by a predetermined amount as a result of axial movement of the shiftable rod. When the workpiece is clamped on the reference face plate by means of the axial movement of clamping means, the tapered portion of the measuring gauge is engaged with the cylindrical bore of the workpiece. Thus, the axial alignment between the workpiece and the spindle is correctly established by confirming the engagement between the tapered portion of the measuring gauge and the cylindrical bore of the workpiece by means of a detector. Thereafter, the tapered portion of the measuring gauge is extracted from the cylindrical bore of the workpiece and then the grinding operation is performed thereon, thereby increasing a degree of grinding accuracy with respect to the cylindrical bore thereof. Furthermore, if the peripheral portion of the workpiece is ground with reference to the cylindrical bore thereof in the other machine tool, the same is concentrically finished with a high degree of accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description when considered in connection with the accompanying drawings, wherein like reference characters designate like or corresponding parts throughout the several views and in which:

FIG. 1 is a cross-sectional view showing a preferred embodiment of a workpiece mounting apparatus according to the present invention;

FIG. 2 is a plan view showing partly a preferred embodiment of a workpiece mounting apparatus of the present invention;

FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2;

FIG. 4 is an enlarged cross-sectional view taken along the line IV-IV in FIG. 3;

FIG. 5 is an schematic view of the control circuit for a positioning cylinder employed within a workpiece mounting apparatus of the present invention;

FIG. 6 is an enlarged cross-sectional view showing a chuck portion in the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings, and more particularly to FIG. 1 thereof, the reference numeral 1 designates a bed on which a spindle head 2 is slidably mounted through a slide carriage 2a. Slidably mounted on a guide surface 4 of the slide carriage 2a is a swivel base 3 with which a main body 5 is connected through a pivot 6 to thereby adjust angularly the direction of the axis of a spindle 7. The spindle 7 is rotatably supported within the main body 5, a V-grooved pulley 8 being keyed to the spindle 7 at the left portion thereof and drivingly rotated by a motor, not shown, through a set of belts 9'. A face plate 10 is fixedly attached to the right side surface of the spindle 7, on which plate a chuck housing 11 is fixedly mounted for rotation therewith. On the right end of the chuck housing 11, a reference face plate 12 is secured to support a workpiece W thereon.

Clamping claws which are indicated by the reference numeral 16 extend outwardly of the chuck housing ll projecting toward the right, as viewed in FIG. 1, through opening holes (in FIG. 6) of the reference face plate 12, at least, at two positions thereon. As shown in FIG. 6, the clamping claws 16 are also pivotably mounted by pivot pins 17 fixed on a supporting disc 15 which is axially pivotably mounted by a pin 15a on the right end of a connecting sleeve 14. Connecting sleeve 14 is operatively connected with an operating member 13 slidably disposed within the spindle 7 in axial alignment therewith. Though the pin 15a is shown as being located on the lower portion of the connectinig sleeve 14, as viewed in FIG. 6, it is actually mounted on the sleeve 14 in the traverse plane perpendicular to the drawing paper. Further, a compression spring 18 is interposed between-one end of each of the clamping claws 1 6.and the reference face plate 12 so that the clamping claws 16 may always be urged to be disengaged from the workpiece W. However, when the operating member 13 is moved toward the left or retracted, in FIG. 6, the clamping claws 16, each having a cam surface 16a thereon, are respectively adapted to clamp the workpiece W on the reference face plate 12 as each clamping claw 16 is urged inwards along the axis of the spindle 7 by the cooperation between the inner face of the opening hole 12a and the cam face 16a.

As shown in FIG. 1, a cylinder 20 is fixedly mounted on the pulley 8 and a piston 21, which is integrally connected with the operating member 13, is reciprocatably received therewithin. A rotatable distributor 22 is provided on the left end portion of the cylinder 20 in order to slidably move the operating member 13 by supplying fluid under pressure into the cylinder 20. That is, passages 22a and 22b are formed within the rotatable distributor 22 and communicate with the right chamber and left chamber of the cylinder 20 respectively. Furthermore, there is fixedly provided a circular plate 39 on the operatinig member 13, at the extreme left end thereof, in such a manner that it may be confronted with an air nozzle 40 to thereby confirm the clamping operation of the workpiece W performed by the clamping claws 16 by means of a detector 44, as seen in FIG. 2.

The construction of a measuring device and an aligning device for the workpiece W will now be described in detail with reference to FIGS. 2, 3 and 6.

A shiftable rod 23 is slidably disposed within the operating member 13 of the spindle 7 and in axial alignment therewith. A measuring gauge 24, which has a tapercd surface 24a, is integrally mounted on the right end or top portion of the shiftable rod 23 and is aligned with the axis of the spindle 7. A receiving member 25 is rotatably mounted on the shiftable rod 23, at the left end portion thereof, through ball bearings but is refrained from axial movement with respect thereto. A first swing arm 27 is fixedly keyed on a first connecting shaft 30, so as to be pivotably moved therethrough, which is rotatably received within a supporting base 26 protruding from the main body 5. A ball 28, which is formed on a guiding shaft 28a fixedly mounted in the first swing arm 27 at the one end thereof, is received within and bears upon the receiving member 25. Therefore, the shiftable rod 23 is axially slidable within the operating member 13 by the pivotable movement of the first swing arm 27 through the ball 28 and the receiving member 25.

As shown in FIG. 2, a spring 41 is tensioned between one end of the first swing arm 27 and the supporting base 26 such that the swing arm may be urged to pivot in a counter-clockwise direction. Rotatably journaled in a bracket 29, threadably mounted on the main body 5, is a. second connecting shaft 32 which is operatively connected with the first connecting shaft 30 through a coupling 31. A pivotable arm is secured to the coupling 31 so as to regulate the shifting movement of the shiftable rod 23. A second swing arm 33 is fixedly mounted on the second connecting shaft 32, at the lower portion thereof, as seen in FIG. 3. Arm 33 is urged in a counter-clockwise direction (FIG. 4) by means of a tension spring 34 interposed between the same and the slide carriage 2a to thereby advance the shiftable rod 23 toward the right by the pivotable movement thereof, as illustrated in FIG. 1. However, while the shiftable rod 23 is being retracted, the pivotable arm 35 is engaged with a limit switch 45 for confirming the original position thereof as seen in FIG. 4.

As seen in FIGS. 4 and 5, a positioning cylinder 36 is firmly attached on the bracket 29 for adjustably pivoting the pivotable arm 35 so as to regulate the advanced position of the shiftable rod 23. In the positioning cylinder 36, a first piston 46 and a second piston 47 are slidably carried and the former is larger with respect to the area subject to the fluid under pressure than the latter. An abutment 48 is secured on a piston rod extended out of the positioning cylinder 36 from the piston 47 at the right end thereof and further, is engageable with the pivotable arm 35. That is, the abutment 48 is axially movable by the sliding movement of the piston 47 in order that the pivoting movement of the pivotable arm 35 may be controlled by the cooperation of the same and the abutment 48, thereby determining the position of the shiftable rod 23 and the measuring gauge 24. Thus, the measuring gauge 24 is displaced into three positions; a retracted position, an intermediate position as shown in FIG. 6, and an advanced position. As shown in FIG. 5, the positioning operation of the measuring gauge 24 is performed by controlling the positioning cylinder 36 by means of the switch of a change-over valve 49. The control of the positioning cylinder 36 will now be described in detail.

In FIGS. 2 and 3, a limit switch, which is indicated by numeral 42, is fixedly mounted on the supporting base 26 for generating a sizing signal by engaging cooperation of the switch with an abutment bolt 43 threadably mounted on the swing arm 27 when the bore of the workpiece W is finished to a predetermined dimension. That is, when a straight portion 24b on the measuring gauge 24 is snugly inserted into the cylindrical bore of the workpiece W by rightward movement of the shiftable rod 23, as seen in FIGS. 2 and 6, the abutment bolt 43 operates the limit switch 42 to issue a sizing signal for stopping the grinding operation.

As shown in FIG. 1, a grinding wheel 19 is rotatably mounted on a wheel head 50 which is installed upon a table 37 slidably mounted on the bed 1. More particularly, the table 37 slides upon the bed 1 in a direction parallel to the axis of the grinding wheel 19 through a reciprocating means, not shown, while the wheel head 50 slides upon the table 37 in a direction perpendicular to the axis of the grinding wheel 19 through a feeding device, not shown. A dog 38 is secured to and extends from the table 37, and is provided for pivotably moving the second swing arm 33 against the urging force of the extension spring 34 through the engagement of the same with the swing arm 33 when the grinding wheel 19 is moved toward the workpiece W for a grinding operation thereon. The shiftable rod 23 is, therefore, retracted toward the original position thereof by the pivotable movement of the second swing arm 33. By this movement of the shiftable rod 23, the measuring gauge 24 is withdrawn from the bore of the workpiece W.

The operation of the workpiece mounting apparatus according to the present invention will now be explained in detail in coordination with the internal grindward the right, in FIG. 1, and arranged apart from the second swing arm 33, to thereby shift the shiftable rod 23 toward the right by the tension force of the springs 34 and 41. However, since the change-over valve 49 is changed into a position I after completion of the previous grinding cycle, the firsit and second pistons 46 and 47 are moved toward the right, as seen in FIG. 5, whereby the abutment 48 on the piston rod of the piston 47 is positioned at the right end position thereof. Thus, the pivotable arm 35 is pivotably moved toward the original position, as shown in FIG. 4, thereby regulating the advancing movement of the shiftable rod and extracting the measuring gauge 24 from the workpiece W.

Furthermore, the clamping claws 16 are pivotably and outwardly moved from the workpiece W by the urging force of the compression spring 18 by shifting the operating member 13 toward the right, as seen in FIG. 1, through the actuation of the piston 21 in the cylinder 20. The workpiece W is therefore unclamped and removed from the reference face plate. Thereafter, when the change-over valve 49 is changed into a position II, as seen in FIG. 5, the pressurized fluid is supplied into a left cylindner 36a and a right cylinder 36b in the positioning cylinder 36 and thus, the first piston 46 is positioned at the right end therein but the second piston 47 is moved toward the piston 46, as seen in FIG. 5. The piston 46 is still immovable even if the piston 47 engages therewith, because the left area subject to the fluid under pressure of the piston 46 is larger than the right area thereof.

Accordingly, the abutment 48 is moved toward the left, as seen in FIG. 5, by the stroke equal to the sliding amount of the second piston 47. The pivotable arm 35 is then pivoted into engagement with the abutment 48 in a counter-clockwise direction, from the position as seen in FIG. 4, by the tension force of the springs 34 and 41 in accordance with the leftward movement of the abutment 48. Therefore, the first and second swing arms 27 and 33 are pivotably moved in the same direction, as seen in FIGS. 2 and 4, by means of the tension forces of the springs 41 and 34, respectively. Therefore, the shiftable rod 23 is advanced through the ball 28 and the receiving member by the pivotable movement of the second swing arm 27.

By the advancing movement of the shiftable rod 23, the measuring gauge 24 is inserted into a cylindrical portion 120 formed in the reference face plate 12 in axial alignment therewith and projecting the tapered surface 24a thereof through a predetermined amount passed a prominent portion 12b of the face plate. The intermediate position of the measuring gauge 24 serves as the position for aligning the workpiece W with the shiftable rod 23, when the workpiece W is loaded on the reference face plate 12 and receivingly held on the measuring gauge 24.

Subsequently, the piston 21 is moved toward the left or retracted position, as seen in FIG. 1, within the cylinder 20 so as to retract the operating member 13. The clamping claws 16 are, therefore, radially inwardly urged and pivoted about the pin 17 by the engagement between the inner face of the opening hole 12a and the cam face 16a, thereby clamping the workpiece W on the reference face plate 12. At this time, the rotational axis of the workpiece W positively coincides with the axis ofthe shiftable rod 23, being based on the tapered surface 24a with which the cylindrical bore of the workpiece W receivingly engages.

When the circular plate 39 is, thereafter, opposed to the nozzle 40 in accordance with the retracting movement of the operating member 13, the detector 44 is operated by the back pressure created within the nozzle 40 and confirmation of clamping of the workpiece W is attained. In response to this confirmation, the change-over valve 49 is changed into the position I resulting in that the pivotable arm 35 is pivoted clockwise by the abutment 48 through the advancing movement of the first and second pistons 46 and 47, as seen in FIG. 4. Thus, the shiftable rod 23 is moved toward the left, in FIG. 1, or retracted into the original position thereof and the tapered portion 24a of the measuring gauge 24 is therefore extracted from the cylindrical bore of the workpiece.

Thereafter, the wheel head 50 is moved toward the workpiece W such that the cylindrical bore of the workpiece is roughly ground by the grinding wheel 19. During this grinding operation, the limit switch 45 is being operated by the pivotable arm 35 in order to keep the shiftable rod 23 in the retracted position. The grinding wheel 19 is therefore not interfered with by the measuring gauge 24 while it is axially traversed several times by a stroke corresponding to the length of the workpiece W.

After the rough grinding operation is completed, the

grinding wheel is dressed by a predetermined amount by means of a dressing tool, not shown. Subsequently, the workpiece W is successively finely ground by the grinding wheel 19 which is axially shifted in a similar manner as described above. Also, the change-over valve 49 is simultaneously changed into a position III when the grinding wheel 19 is: moved away from the workpiece W and the fluid under pressure is admitted into the right chamber of the cylinder 36 and exhausted from the chambers 35a, 361;, as seen in FIG. 5. Consequently, the first and second pistons 46 and 47 are moved toward the left, thereby displacing the abutment 48 from the position shown in FIG. 5. The swing arms 27 and 33 are pivotally moved in a counter-clockwise direction by the urging force of the springs 41 and 34 and thus, when the shiftable rod 23 is advanced, the measuring gauge 24 is moved toward the cylindrical bore of the workpiece W.

At this time, if the bore of the workpiece W is not still being finished into a predetermined diameter, the straight portion 24b of the measuring gauge 24 is not inserted into the bore thereof. Therefore, the grinding wheel 19 is further repeatably moved toward and away from the workpiece through the sliding movement of the table 37. Moreover, the measuring gauge 24 is also extracted from the workpiece W by the swing arm 27 through the engagement between the second swing arm 33 and the dog 38 on the table 37 when the grinding wheel 19 is moved toward the workpiece W. When the grinding wheel 19 is moved away from the workpiece W, the measuring gauge 24 is shifted toward the workpiece W.

As soon as the bore of the workpiece W is completed into the predetermined diameter, the straight portion 24b is receivingly admitted into the bore thereof. When the straight portion 24b is located at the advanced position thereof, the limit switch 42 is actuated by the abutment bolt 43 on the swing arm 27 thereby generating the sizing signal. The grinding wheel 19 is moved away from the workpiece which is, in return, unclamped from the reference face plate 12 by releasing of the clamping claws 16.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings, It is to be understood therefore, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

We claim:

1. An apparatus for mounting a workpiece in an internal grinding machine having a bed, a spindle head slidably mounted upon said .bed, a' table slidably mounted upon said bed and movable toward and away from said spindle head, and a whheel head mounted upon said table and rotatably carrying a grinding wheel, comprising:

a main body of said spindle head;

a spindle rotatably mounted on said main body;

a chuck housing fixedly mounted on said spindle at one end thereof and provided with a reference face;

clamping means axially slidably mounted within said spindle and provided for clamping the workpiece on the reference face of said chuck housing;

aligning means disposed within said spindle in axial alignment therewith and having an aligning portion for establishing alignment between the axis of the workpiece and the axis of said spindle through engagement with the cylindrical bore of the workpiece when the workpiece is clamped on said reference face by means of said clamping means;

a measuring gauge integrally provided on said aligning means and adapted to be snugly inserted into the cylindrical bore of the workpiece to confirm the completion of the machining operation when the bore is machined into a finished size; and

positioning means mounted on said main body and capable of selectively projecting said alignment means from the one end of said chuck housing through first and second predetermined distances so as to align the workpiece with said spindle by said aligning portion and confirm the completion of the machining operation by said measuring gauge.

2. An apparatus for mounting a workpiece according to claim 1, wherein said aligning means comprises:

a shiftable rod slidably mounted within said spindle and provided with said aligning portion and said measuring gauge at the one end thereof in co-axial alignment with said spindle; and wherein said positioning means comprises:

a hydraulic actuator connected with said shiftable rod for regulating projected positions of said aligning portion and said measuring gauge; and

spring means for urging said shiftable rod so that said mesuring gauge may be yieldably projected from the reference face of said chuck housing through said second predetermined distance determined by said hydraulic actuator.

3. An apparatus for mounting a workpiece according to claim 1, wherein said clamping means comprises:

an operating member slidably mounted within said spindle in axial alignment therewith;

a supporting member axially pivotably mounted on said operating member;

a clamping claw pivotably mounted on said supporting member and urgingly held by means ofpushing control cylinder means operably connected with said operating member for engaging said clamping claw with the workpiece against the urging force of said pushing means.

4. An apparatus for mounting a workpiece according to claim 3, wherein said control cylinder means comprises:

a cylinder integrally connected with said spindle;

a piston fixedly mounted on said operating member and slidably received within said cylinder so as to move said clamping claw toward the periphery of the workpiece for clamping the same on the reference face of said chuck housing; and

a rotatable distributor attached to said cylinder for introducing the fluid under pressure to axially move said piston.

5. An apparatus for mounting a workpiece according to claim 1, wherein said positioning means includes shifting means operably connected with said aligning means so as to move the same toward and away from the cylindrical bore of the workpiece and said shifting means comprises a shiftable rod slidably mounted within said spindle and operably connected with said aligning means:

a receiving member rotatably journaled on said shiftable rod at the other end thereof and refrained from axial movement with respect thereto;

a connecting shaft rotatably supported within said main body;

a first swing arm secured to the one end of said connecting shaft and operatively connected with said shiftable rod for axially sliding the same through said receiving member;

a second swing arm fixedly mounted on the other end of said connecting shaft;

a pivotable arm secured on said connecting shaft for regulating the rotational movement of said first swing arm;

spring means interposed between said second swing arm and said bed so as to rotatably move said second swing arm by means of the urging force thereof.

6. An apparatus for mounting a workpiece according to claim 5, wherein said positioning means further includes control means operably connected with said shifting means for controlling the advancing position of said shiftable rod and said control means comprises:

a cylinder provided on said main body;

a first piston and second piston slidably received within said cylinder and different from each other with respect to the area subject to the fluid under pressure;

change-over valve means arranged to change the direction of fluid supplied to said cylinder and control the slidable movement of said first and second pistons;

an abutment integrally connected to said second piston and protruding outwardly of said cylinder for regulating the pivoting movement of said pivotable arm through the engagement therewith in accor dance with controlling of the axial movement of said second piston; and

switching means provided on said main body for detecting the original position of said shiftable rod. 

1. An apparatus for mounting a workpiece in an internal grinding machine having a bed, a spindle head slidably mounted upon said bed, a table slidably mounted upon said bed and movable toward and away from said spindle head, and a whheel head mounted upon said table and rotatably carrying a grinding wheel, comprising: a main body of said spindle head; a spindle rotatably mounted on said main body; a chuck housing fixedly mounted on said spindle at one end thereof and provided with a reference face; clamping means axially slidably mounted within said spindle and provided for clamping the workpiece on the reference face of said chuck housing; aligning means disposed within said spindle in axial alignment therewith and having an aligning portion for establishing alignment between the axis of the workpiece and the axis of said spindle through engagement with the cylindrical bore of the workpiece when the workpiece is clamped on said reference face by means of said clamping means; a measuring gauge integrally provided on said aligning means and adapted to be snugly inserted into the cylindrical bore of the workpiece to confirm the completion of the machining operation when the bore is machined into a finished size; and positioning means mounted on said main body and capable of selectively projecting said alignment means from the one end of said chuck housing through first and second predetermined distances so as to align the workpiece with said spindle by said aligning portion and confirm the completion of the machining operation by said measuring gauge.
 2. An apparatus for mounting a workpiece according to claim 1, wherein said aligning means comprises: a shiftable rod slidably mounted within said spindle and provided with said aligning portion and said measuring gauge at the one end thereof in co-axial alignment with said spindle; and wherein said positioning means comprises: a hydraulic actuator connected with said shiftable rod for regulating projected positions of said aligning portion and said measuring gauge; and spring means for urging said shiftable rod so that said mesuring gauge may be yieldably projected from the reference face of said chuck housing through said second predetermined distance determined by said hydraulic actuator.
 3. An apparatus for mounting a workpiece according to claim 1, wherein said clamping means comprises: an operating member slidably mounted within said spindle in axial alignment therewith; a supporting member axially pivotably mounted on said operating member; a clamping claw pivotably mounted on said supporting member and urgingly held by means of pushing means interposed between the same and said chuck housing so as to be disengaged from the workpiece; control cylinder means operably connected with said operating member for engaging said clamping claw with the workpiece against the urging force of said pushing means.
 4. An apparatus for mounting a workpiece according to claim 3, wherein said control cylinder means comprises: a cylinder integrally connected with said spindle; a piston fixedly mounted on said operating member and slidably received within said cylinder so as to move said clamping claw toward the periphery of the workpiece for clamping the same on the reference face of said chuck housing; and a rotatable distributor attached to said cylinder for introducing the fluid under pressure to axially move said piston.
 5. An apparatus for mounting a workpiece according to claim 1, wherein said positioning means includes shifting means operably connected with said aligning means so as to move the same toward and away from the cylindrical bore of the workpiece and said shifting means comprises a shiftable rod slidably mounted within said spindle and operably connected with said aligning means: a receiving member rotatably journaled on said shiftable rod at the other end thereof and refrained from axial movement with respect thereto; a connecting shaft rotatably supported within said main body; a first swing arm secured to the one end of said connecting shaft and operatively connected with said shiftable rod for axially sliding the same through said receiving member; a second swing arm fixedly mounted on the other end of said connecting shaft; a pivotable arm secured on said connecting shaft for regulating the rotational movement of said first swing arm; spring means interposed between said second swing arm and said bed so as to rotatably move said second swing arm by means of the urging force thereof.
 6. An apparatus for mounting a workpiece according to claim 5, wherein said positioning means further includes control means operably connected with said shifting means for controlling the advancing position of said shiftable rod and said control means comprises: a cylinder provided on said main body; a first piston and second piston slidably received within said cylinder and different from each other with respect to the area subject to the fluid under pressure; change-over valve means arranged to change the direction of fluid supplied to said cylinder and control the slidable movement of said first and second pistons; an abutment integrally connected to said second piston and protruding outwardly of said cylinder for regulating the pivoting movement of said pivotable arm through the engagement therewith in accordance with controlling of the axial movement of said second piston; and switching means provided on said main body for detecting the original position of said shiftable rod. 